Department tardy in letter writing saga

The immigration department boss has vowed to investigate how thousands of goodwill letters addressed to asylum seekers in offshore detention were returned unopened to their Australian senders.

Prominent barrister Julian Burnside, who initiated the public letter writing campaign, received three boxes of the unopened letters marked returned to sender last year.

Department secretary Michael Pezzullo acknowledged the department had been "tardy" in responding to Mr Burnside's requests for an explanation and promised to personally intervene.